In existing implantable arrhythmia control systems the high voltage switches are controlled by transformer coupled control signals. An example of an implantable arrhythmia control system is described in U.S. Pat. No. 4,960,123 to P. J. Maker, entitled "Differentiating between Arrhythmia and Noise in an Arrhythmia Control System". The transformer coupling techniques for controlling the high voltage switches in existing devices have been found to possess a number of disadvantages. These include the high volume of the coupling transformers, the cumbersome mechanical structure of these transformers and, additionally, the high susceptibility of the core of the transformer to external magnetic fields.
It is aesthetically advantageous, and of greater comfort to a patient or recipient of an implantable medical device, to reduce the volume and the weight of the device. Additionally, reducing the mechanical complexity of the components used in implantable devices not only reduces the cost but also improves the functional reliability of the system. It is of further advantage to the recipient of an implantable device to reduce the susceptibility of the device to magnetic interference which frequently occurs in normal living and work environments, as well as in hospitals or clinics, especially during the delivery of certain types of medical therapies and other treatments.
Accordingly, it is an object of the present invention to provide an improved circuit for driving high voltage switches in implantable pacemaker/defibrillators and other medical devices by incorporating capacitively coupled control signals in place of the transformer coupling techniques used in prior art pacemaker/defibrillators and other medical devices.
It is a further object of the invention to provide an apparatus which offers to patients or recipients of pace-maker/defibrillators and other implantable medical devices the advantages of lower costs, reduced volume, greater functional reliability and lower susceptibility to the hazards of electromagnetic interference.
It is a still further object of the invention to enhance the efficiency of such a device by the design of control circuitry which allows the output switch to be turned on and turned off in a very short time, thus preventing turn-on/turn-off transient currents from overheating the output switch with possible resultant damage to the switch. This is especially important in implantable medical devices to avoid damage to critical electronic components.
Another object of the invention is to provide a device for capacitive control of a high voltage output switch wherein the circuit has a very high common mode rejection ratio. As a result, the common mode switching high voltage transients do not lead to false switching of the high voltage switch. The invention aims to improve patient safety by the implementation of such a factor in its circuitry.
It is yet another object of the invention to reduce the peak current consumption of implantable defibrillator/pacemakers and other devices by providing a high voltage output switch driving circuit having reduced power consumption, thus preventing the output switch driving circuit from overloading the power supply. Hence, lower current, simpler design supplies can be used. As a result, by means of appropriate circuit implementation, a further reduction in volume of the implantable device is attainable.